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Abstract

With increasing offshore wind penetration levels, more secure and flexible offshore electrical transmission systems are needed to ensure security of supply to onshore users. When considering long distances of electrical power transmission, HVDC grids based on the modular multilevel converter (MMC) are a solution for present and future large scale offshore wind integration. As HVDC grids are developing into large and complex systems, dynamic analyses are useful to gain knowledge on the interactions between the different components in the grids. This paper uses the open source tool OpenModelica as modeling environment to demonstrate the potential of the tool in modeling such HVDC systems. A three-terminal HVDC system with offshore wind and energy storage integration is implemented in OpenModelica, and the dynamics of the system are investigated through four simulation cases. The main focus of this paper is dynamics and operation related to the HVDC system. The simulation results show that the MMCs can improve the most rapid power fluctuations using its internal storage capabilities, while an external energy storage system provides a more constant power flow over more extensive periods, in addition to improving the operation of the HVDC system. All models used in this paper are made publicly available to anyone for any purpose, including future studies of larger HVDC grids.